Asset management techniques for transformers

In power system reliability evaluation, alternating renewal process is generally used to model the failure and repair cycle of a component. This means that after repair, the component is assumed to be restored to as good as new condition from the reliability perspective. However, in practice, there may exist an aging trend in some components as they grow old. This paper describes how aging characteristics of components may impact the calculation of commonly used reliability indices such as loss of load expectation (LOLE). In order to construct the system failure and repair history of components, sequential Monte Carlo simulation method using stochastic point process modeling is introduced. Three methods are described for this purpose and this methodology is applied to the single area IEEE reliability test system. The results are analyzed and compared.

Reliability Modeling and Simulation in Power Systems With Aging Characteristics

An algorithm for integrating uncertain parameters in Markov analysis is proposed. Fuzzy Markov models for aging equipment and substations are developed in which the transition rates/probabilities with uncertainty are represented by fuzzy membership functions. An extension principle and nonlinear optimization-based approaches are utilized for calculation of fuzzy reliability indices. Sensitivity studies for analyzing the impact of various fuzzy membership functions on reliability indices are provided, and the characteristics of the results are discussed. The fuzzy Markov model presented in this paper has valuable application in extending current Markov analysis with the ability to incorporate uncertainties associated with data collected on maintenance activities, etc.

Reliability Evaluation of Equipment and Substations With Fuzzy Markov Processes

This paper proposes a novel mechanism for unit maintenance scheduling (UMS) in the deregulated environment, based on the different functions of power producers and the independent system operator (ISO). The proposed scheme aims to achieve a tradeoff between ensuring the producers' benefits and maintaining the system reliability, providing satisfactory maintenance windows and cost-reflective reward/charge to individual producers. The proposed scheme has a three-step mechanism. Firstly, power producers have to evaluate the potential benefits of energy-selling profits versus maintenance costs and expected renewal costs for each available outage window, considering the impacts of unexpected unit failures. Based on the resultant costs/benefits, power producers will submit a set of maintenance bidding costs (MBCs) for its owned units to the ISO, indicating their preference of either continuous operating or maintenance outage during the corresponding periods. Subsequently, the ISO schedules their outage periods to attain a fine balance among the bidding costs, the satisfactory degrees (SDs) of generating units and the possible load curtailment. Thirdly, as a nonprofit organization, the ISO has to settle the final expenditure of individual power producers in terms of an appropriate SD -based cost settlement method. The IEEE-RTS system is used to demonstrate the key features of the proposed mechanism in practical applications, including its fairness, simplicity and effectiveness.

A Competitive Mechanism of Unit Maintenance Scheduling in a Deregulated Environment

Conventional VAR compensation devices such as capacitor banks and synchronous condensers, after long periods of service, have become aged and less effective to satisfy stringent requirement of short-term voltage stability in high-level wind power penetrated power systems. STATCOMs with a rapid and dynamic reactive power support capability can be an ideal alternative, when combined with a proper equipment retirement and upgrades scheme. This paper proposes a systematic approach for optimal dynamic VAR resource planning and upgrading for a power system with increased wind power penetration and equipment retirement. The problem is constituted by two parts that are aged equipment retirement and new equipment placement. A multiobjective optimization model is proposed to minimize three objectives: the cost of retirement and upgrades, the index of proximity to steady-state voltage collapse, and the index of transient voltage unaccepted performance. To simulate real-world operating situation, multiple contingencies and uncertain dynamic load models are taken into account. Furthermore, low- and high-voltage ride through abilities for wind farms are modeled. The proposed model is tested on the New England 39-bus test system.

Retirement-Driven Dynamic VAR Planning for Voltage Stability Enhancement of Power Systems With High-Level Wind Power

This article discussed the issues around power system equipment aging, including concepts of equipment lifetime, approaches to estimating the mean life and age, Weibull and normal-distribution-based models to assess the end-of-life failure probability. The relationship between aging and maintenance activities, limitations of maintenance in extending equipment life, and determination of timing of retirement were also discussed. A few examples showing actual data of transformers, cables, and reactors at BCTC have been presented. Maintenance activities can extend the life of equipment but could be very costly for equipment at their end-of-life stage. A compromise between maintenance and replacement must be carefully considered. RCM and probabilistic analysis approaches are available for utilities to guide maintenance activities and manage aged assets in a more efficient and economic manner

E. Vaahedi

Papers

Power system equipment aging